Compressor control apparatus



Nov. 6, 1962 R. F. WILLIAMS 3,062,433

COMPRESSOR CONTROL APPARATUS Filed June 7, 1957 2 Sheets-Sheet l INVENTOR: RAYMOND F. WILLIAMS BY a /W ATTORNEY Nov. 6, 1962 R. F. WILLIAMS COMPRESSOR CONTROL APPARATUS 2 Sheets-Sheet 2 Filed June 7, 1957 MM m Emu v QW 1 m E .M m M 20 W FHA .R

VIII/11127111) COMPRESSOR FIG. 6.

ATTORNEY 3,062,433 Patented Nov. 6, 1962 time Ware

Filed June 7, 1957, Ser. No. 664,362 1 Claim. (Cl. 230-24) This invention relates to controls for air compressors and more particularly to a control unit for a plurality of air compressors having means for loading and unloading the individual compressors.

Mold-compressor controls are used in installations wherein the demand for compressed air fluctuates and are designed to control the compressors to provide only as much air as may be demanded.

Heretofore, compressor controls for a multi-compressor installation have used one of two methods of control. The first method uses a separate pressure responsive mechanism for each compressor so that each compressor loads and unloads at a predetermined pressure in the air receiver or air storage tank. As the pressure in the air receiver decreases, the first compressor in the installation is loaded. If the first compressor cannot meet the demand and the pressure in the receiver continues to drop, a second compressor is loaded. This procedure continues with successive compressors being loaded at successively lower receiver pressures until the demand for air is met. As the demand for air decreases, the pressure in the air receiver increases and the compressors are successively unloaded in the inverse order of the loading described above. The principal disadvantage of the method outlined above is that the first compressor runs loaded practically all the time while the last compressor in the system is only loaded when the demand for air is at a maximum which normally is an infrequent occurrence.

The second method of multi-compressor control uses a pressure switch or pressure responsive mechanism which loads and unloads the whole bank of compressors simultaneously. This method has the advantage of giving each compressor equal wear but causes violent and frequent power surges which create a variable demand on power transmission lines and may, in many industrial plants, cause severe voltage fluctuations throughout the entire plant.

The compressor control unit described herein overcomes the disadvantages of the two methods of multicompressor control heretofore described to provide even distribution of work and wear over all compressors in an installation While eliminating the violent power surges.

Accordingly, it is an object of this invention to provide a control unit for a plurality of compressors wherein the work load on the compressors is evenly distributed over the compressors.

It is another object of this invention to provide a control system for a battery of compressors whereby each compressor will operate independently of the others during a specific interval of time.

It is another object of this invention to provide a control unit for a plurality of compressors whereby the compressors are loaded and unloaded one at a time in order to balance the output of the compressors with the demand for compressed air.

It is a more specific object of this invention to provide, in a compressor installation, control means for automatically recycling the order in which the compressors are successively loaded and unloaded to meet the demands of the air system.

Further objects and advantages of this invention will become apparent from the following specification and the accompanying drawings in which:

'FIG. 1 is a front elevation view of the compressor control unit which is the subject of this invention;

FIG. 2 is an enlarged view of the recycling mechanism of the compressor control unit taken along the line IIH of FIG. 1;

FIG. 3 is a view of the cam and switch elements of the recycling mechanism taken on the line III-III of FIG. 2.

FIG. 4 is a diagrammatic representation of the control unit of FIG. 1;

FIG. 5 is a diagrammatic representation of an air compressor installation utilizing the control unit of this invention; and

FIG. 6 is a sectional view of a compressor unloading valve of a type adaptable for use with the control unit of this invention.

Referring to the drawings, a control unit 1 is contained within a rectangular housing. Within the housing is a. pressure responsive element 2 containing a diaphragm 3 connected by means of a conduit 4 to a common air receiver of an air compressor installation. Pressure from the air receiver (FIG. 5) acts on diaphragm 3 to move a lever 5 by means of a movable element 6 having a knife edge 7 acting against the lever 5. Lever 5 is fulcrumed at knife edge 8 and is free to pivot within limits about this point depending on the pressure acting upon diaphragm 3. Lever 5 is loaded with weights 9 and a Vernier weight 10 in the manner of a beam type scales. The Weights 9 and 10 acting upon the lever 5 may be varied through a wide range to balance the lever against a predetermined air pressure active upon diaphragm 3. Once in balance at a predetermined air pressure, any increase or decrease in pressure active upon diaphragm 3 will raise or lower lever 5 in response thereto.

Mounted on the lever 5 midway of its length and transversely of the longitudinal axis of the lever 6 is a cam assembly 11 comprising a transverse shaft 12 having a plurality of eccentric earns 13 adjustably mounted on said shaft. In the illustrative embodiment herein shown, four earns 13 are illustrated which coact with four switches to control four compressors, as hereinafter described; but it will be obvious that the number of cams, switches and compressors may be varied over a wide range, provided at least two cams, switches, and compressors are used to.

obtain the results provided by this invention.

Attached to the housing beneath the lever 5 are four electric switch elements 14, of the type sold under the tradename micro-switch, which are readily available standard components. The switches 14 are each aligned with one of the cams 13 on shaft 12 and carried by the lever 5. The switches 14 each have an elongated resilient contact arm 14a adapted to actuate the switch upon a slight depression of arm 14a but permitting considerable further depression or over-travel of the arm as cams 13 rotate, as hereinafter described, without breaking the electrical circuit completed by the initial actuation of the switch. The switches 14 each control a magnetic unloader 15 of a type well known in the art of air compressors and compressor controls. For the purpose of this specification, it is suflicient to point out that when one of the switches 14 is closed, a coil 16 is energized to activate a magnetic element enclosed therein. As the magnetic switch closes, a three-way valve 17 is closed interrupting the flow of air pressure from the air receiver and venting to atmosphere the pressure acting upon the suction unloading valve (FIG. 6) of one of the compressors in the bank of compressors. Air from the receiver is admitted to the magnetic unloaders from a manifold 18 having conduits 19 connecting the manifold to one side of each of the three-way valves 17. Conduits 20 on the other side of each of the three-way valves conduct manifold or air receiver pressure to the individual compressors.

Each of the magnetic unloaders is provided with an indicating electric bulb 21 to indicate whether the compressor controlled by each of the magnetic unloaders is running loaded or unloaded.

When a magnetic unloader 15 is not energized air is supplied to the compressor unloading valves to unload the compressors. When a magnetic unloader 15 is energized by the switch 14 controlling the same, the air pressure active upon the unloading valve is interrupted to load the compressor.

The eccentric cams 13 are adjustable by means of set screws (not shown) on the shaft 12 and are normally adjusted so that as the lever 5 moves from its uppermost position to its lowermost position upon a reduction in pressure active upon diaphragm 3, the earns 13 successively contact the switches 14 until in the lowermost position of lever 5 all four switches 14 are closed to load all the compressors controlled by the unit which is the subject of this invention. Electric current for the operation of the control unit is supplied from a source not shown through an on-off switch 22.

FIG. 6 illustrates a suction unloading valve 23 of a well-known type having a resilient diaphragm 24 one side of which is adapted for connection to a conduit from control unit 1. A compressor having a valve of this type is unloaded when fluid pressure active against diaphragm 24 pushes a plunger 25 against the biasing pressure of a compression spring 26. An element 27 carried by plunger 25 and having a plurality of spaced fingers 28 serves to hold one of the suction valve plates 29 of the compressor away from its seat permitting air to move into and out of the compressor without being compressed. When the three-way valve 17 in control unit 1 controlling this suction unloading valve is closed, the pressure active upon diaphragm 24 is interrupted. Plunger 25 then retracts under the urging of spring 26 retracting element 27 and fingers 28 therewith to allow the suction valve plates 29 to move on and ofi their seats in a normal manner.

In operation of the unit illustrated, as shown in FIG. 2, reading from left to right and with the rotatable shaft 12 stationary, the cams 13 will engage switches 14 in the order of 1-4-32. In other words, with the lever 5 in its uppermost position, none of the cams contact the switches 14. When the air receiver pressure active upon diaphragm 3 drops slightly, lever 5 lowers until the first cam 13 engages its switch 14 thus loading the first compressor. If one compressor can meet the demand for air from the receiver the lever 5 will be balanced and the first compressor will remain loaded until the demand for air either increases or decreases. If the demand for air is not met or subsequently increases the air receiver pressure drops further consequently lever 5 lowers further until the next cam contacts its switch and a second compressor is loaded along with the first compressor.

If additional air is required and lever 5 drops further, third and fourth compressors will be successively and cumulatively loaded in the same manner. Only the number of compressors required to meet the demand for air from the air receiver will be loaded. As the demand decreases the compressors will, of course, be successively and cumulatively unloaded in reverse order.

However, as described above, with a variable demand for air, the first compressor will be loaded a considerable portion of any given period while the fourth compressor will only be loaded during the infrequent intervals when the air demand is at its peak. To distribute the load evenly over the four compressors, control means are provided to automatically alternate the order of loading the compressors over a relatively short period of time. The control means for alternating or recycling the order of loading is an electric motor 30 which continuously rotates the shaft 12 on which the earns 13 are eccentrically mounted. I have used a motor designed to make one complete revolution every six minutes and will describe d the results accordingly although it may be desirable that the speed of the motor be selectively variable.

Assuming a continuous demand for air which can be met by one compressor, the first cam causes the first compressor, to be loaded as hereinbefore described. With shaft 12 being continuously rotated the first compressor will remain loaded for a time interval of about one and one-half minutes until the first cam is rotated enough to disengage from or open the first switch thereby unloading the first compressor. About the same time as the first cam disengages from its switch, the second cam will contact the second switch to load the second compressor. Further rotation of the shaft 12 will cause the second compressor to be unloaded and the third compressor to be loaded; and eventually the third compressor will be unloaded and the fourth loaded in the same manner. During the 360 degree rotation of the shaft 12 during a six minute period, each of the four compressors will be successively loaded and unloaded until the first compressor is again loaded to complete the cycle.

It will be obvious that for any condition of loading of the compressors, except when all of the compressors are either loaded or unloaded, the automatically recycling mechanism evenly distributes the load among all the compressors; yet at any given moment only the number of compressors necessary to meet the demand for air will be loaded.

While the control system hcreinbefore described was designed primarily for the control of four compressors, it may be used for any number of compressors by either eliminating or adding cams, switches and magnetic unloaders or by piping more than one compressor to any or all of the magnetic unloaders in the control unit.

In the foregoing description, the term compressor has been used as defining an independent unit of the piston type, having at least one compression cylinder. In a broad sense, each cylinder of a compressor unit, either piston type or rotary type, is a compressor and it is in that sense that the term compressor is used in the appended claims. Hence, the control unit herein described may also be used to recycle the loading of one single stage or multiple stage multi-cylinder compressor wherein each cylinder is equipped with an unloading mechanism and may also be used to recycle the loading and unloading of double acting compressor of the type having clearance pockets controlled by pressure responsive valves.

It will be readily apparent that the invention herein disclosed may be readily adapted to control compressors having different types of unloading mechanisms without departing from the scope of the invention hereinafter claimed.

I claim as my invention:

In an air compressor apparatus: a plurality of air compressors; an air receiver connected to said compressors; an unloading mechanism for each of said compressors; a control unit for said unloading mechanisms comprising a housing, a plurality of switches mounted in said housing for actuating respective unloading mechanisms, a lever mounted in said housing for limited pivotal movement with respect to said switches, a cam assembly carried by said lever for engagement with said switches, said cam assembly including a rotatable shaft, electric motor means operationally independent from said compressors and driveably connected to said shaft for rotating the same at a selected speed predeterminable without regard to compressor speed, and a plurality of camming means mounted on said shaft and having cam surfaces for engaging respective switches; said cam surfaces being positioned with respect to each other to engage said switches cumulatively when said cam assembly is pivoted toward said switches; said cam surfaces being positioned with respect to each other to engage said switches sequentially when said cam means is rotated by said shaft; and, means responsive to air pressure in said receiver for pivoting said lever and said cam assembly.

References Cited in the file of this patent UNITED STATES PATENTS Peters Apr. 2, 19'18 Carlsson May 7, 1918 Madden Dec. 30, 1924 Riesner Apr. 6, 1926 Raymond Oct. 23, 1934 Welcher Dec. 13, 1960 

